The present invention relates to SAR interferometry, and more particularly, to hyper-precision SAR interferometry using a dual-antenna multi-pass SAR system and processing method.
Previous SAR interferometers were either dual antenna systems, such as are described in L. C. Graham, "Synthetic Interferometer Radar for Topographic Mapping", Proc. IEEE, Vol. 64, pp. 763-768, June 1974, achieving limited relative accuracy, or were derived from post processing of data from pass-to-pass, as is described by F. Li and R. Goldstein, "Studies of Multi-baseline Spaceborne Interferometric Synthetic Aperture Radars", IEEE Trans. Geocsience and Remote Sensing, Vol. 28, pp. 88-97, January 1990, achieving limited absolute accuracy due to phase ambiguities and lack of relative calibration.
The synthesis of dual-antenna and multi-pass interferometry is technically difficult because of problems in effectively combining the two types of data. A process of simply averaging data from different passes is not effective because the phase functions have imprecisely known differences in scale (interferometer baseline), they have unknown systematic error terms (at least affine in range-azimuth), they include possibly severe random noise, and, after all of these degradations, are only measurable modulo 2.pi.. This also precludes the superficial application of traditional ambiguity resolution techniques, for example the independent application of the Chinese Remainder Theorem in each range-azimuth cell. Selecting the phase difference basically from one image pair or another, as a function of phase variance, also fails for the same reasons.